Conventionally, failures in photographing have resulted mostly from camera shake and out-of-focus state. In recent years, however, the automatic focusing mechanism has been employed in most cameras and as the focusing accuracy of the automatic focusing mechanism improves, the failure in photographing due to out-of-focus state has been virtually solved. On the other hand, lens systems which come standard on cameras have shifted from fixed focal length lens systems to zoom lens systems. As a result, at present, it is no exaggeration to say that failures in photographing are caused by camera shake. For this reason, a camera shake compensation function is indispensable to zoom lens systems.
To solve this problem, Japanese Laid-open Patent Application No. H6-337374 discloses a two-component zoom lens system of negative, positive configuration in which the whole of the second lens unit is parallelly decentered to compensate for camera shake. Japanese Laid-open Patent Application No. H7-64025 discloses a two-component zoom lens system of negative, positive configuration in which the second lens unit is divided into a front lens unit having a positive optical power and a rear lens unit having a negative optical power and the front lens unit having a positive optical power is parallelly decentered to compensate for camera shake.
However, in Japanese Laid-open Patent Application No. H6-337374, since the whole of the second lens unit is moved as a camera shake compensation unit, the load imposed on the camera shake compensation drive system is heavy. In Japanese Laid-open Patent Application No. H7-64025, since evaluation is performed with a camera shake angle of 0.2 degrees, camera shake cannot be completely compensated for when a greater camera shake occurs.